Processing aids in preparation of nbr flexible magnets



United States Patent 3,428,603 PROCESSING AIDS IN PREPARATION OF NBR FLEXIBLE MAGNETS William J. Kroenke, Brecksville, Ohio, assiguor to The B. F. Goodrich Company, New York, N.Y., a corporation of New York No Drawing. Filed Jan. 16, 1967, Ser. No. 609,358 US. Cl. 252-6254 2 Claims Int. Cl. H011 1/11, 1/113, 1/117 ABSTRACT OF THE DISCLOSURE Alkyl amine salts of alkyl iminopolyacetic acids and derivatives thereof assist in the combination of large volumes of fine barium ferrite particles with butadieneacrylonitrile synthetic rubber polymers. The heavily loaded rubber stocks are then readily extruded into solid shapes for use as flexible magnets.

BACKGROUND OF THE INVENTION Solid metallic magnets are known. Solid ceramic magnets are known. For some uses, particularly where the magnets must be small and rounded or curved in shape, these solid magnets are not always useful. So-called flexible magnets have been developed which, in addition to this improvement, are less costly than rigid magnets. Flexible magnets consist of an elastomeric binder containing many particles of a magnetic compound. The binder has a degree of flexibility, allowing the magnet to be bent, curved or arced to fit a contour, and the magnetic particles or powder, dispersed throughout the binder, provide the magnetic strength desired. These bonded magnets are less hard and brittle than metal or ceramic magnets. They can be readily cut and shaped by punching, extruding, drilling and the like. Rubbery polymers are particularly favored as binder materials. Finely ground barium ferrite is particularly favored as a magnetic material. A problem that exists in making this type of magnet is that one needs a very high (above 60% by volume) concentration of magnetic particles dispersed in the rubber binder matrix to obtain useful magnetic strength. The magnetically strongest magnet would consist solely of magnetic particles and would contain no binder at all, but such a material has no cohesive binding strength unless it is fired at very high temperatures, and it then would be a rigid structure. At the 60-65 volume percent levels of magnetic powder loading generally required for high magnetic strength, the binders cohesive strength is severely weakened. United States Patent 3,121,131 describes the making of magnets by milling 65% by volume barium ferrite into natural rubber. This mixture is useful in magnetic strength, but lacks physical strength to allow it to be extruded through a die to a desired shape. Crumbling occurs when the matrix rubber is loaded with a magnetic filler to the extent that the matrix can no longer wet the filler particles to bind them. The patent teaches one to overcome this problem by milling the stock into thin sheets which are then plied to a desired thickness and laminated. The need to ply and laminate thin sheets to a desired thickness which can then be cut to a desired shape, leads to extra operations and higher costs. This invention provides a process for making NBR polymer binder containing a high volume percent barium ferrite that can be extruded through dies of any desired shape and then cut to any desired length.

SUMMARY OF THE INVENTION Among the rubbery polymers that one desires to use as binders for finely ground magnetic materials are the synthetic nitrile rubbers known as NBR. NBR polymers are particularly useful when the magnets will be employed in conditions where resistance to oil is important. Commercial nitrile rubbers, acrylonitrile-butadiene copolymers, noted for their resistance to oils and petroleum fractions are available. Nitrile rubbers containing a high weight percent acrylonitrile (50%60%) and a medium weight percent acrylonitrile (25 %-49%) are most useful. Nitrile rubbers with low weight percent acrylonitrile (less than 25%) do exhibit resistance to oils, and if the proposed exposure to oil is fairly low, these rubbers may also be used as binders for flexible magnet stocks. In general the resistance of the nitrile rubber to oil increases as the weight percent acrylonitrile in the copolymer increases.

To achieve sufficiently high magnetic strength, 60-65 volume percent barium ferrite must be combined with the NBR binders. While this amount of barium ferrite can be milled into natural rubber, as shown in Patent 3,121,- 131, this natural rubber-ferrite mixture does not have strength to enable one to extrude it in thick shapes of A or more thickness. If NBR is substituted for natural rubber in the formation of the rubber-ferrite mix, it is found that only about 50 volume percent barium ferrite can be added before the mixture loses cohesive strength and becomes brittle and crumbles. In addition, the material has a low maximum energy product of about 100,000 gauss-oersteds whereas a value of at least 700,000 gauss-oersteds is required for a useful product. Higher amounts of ferrite cause the stocks to crumble and fall from the mills. These stocks cannot even be sheeted in thin slabs as the prior art patent teaches with the natural rubber-ferrite mixtures. The use of processing aids with rubber stocks is known. Processing aids are not universal in nature, however. A processing aid for natural rubber will not necessarily improve the processing of a given synthetic rubber. This invention provides processing aids which enable one to mill 60-65 volume percent barium ferrite into NBR polymers to provide compositions which can be extruded into desired shapes for use as magnetic materials.

The processing aids discovered for this use are soluble in or compatible with conjugated diolefin rubbers. They comprise materials having the structure wherein R is a hydrocarbon group having from 6 to 20 carbon atoms, R is selected from the group consisting of hydrogen, CH COOH, and CH COOH NR". R is a saturated hydrocarbon group having from 2 to 10 carbon atoms, R' is a hydrocarbon group having 6-20 carbon atoms, x is a number of from 0 to 1, y is a number of from 1 to 2 and z is a number of from 0 to 1. Whenxis 0,yis 1, andzis0.Whenxis 1,yis 1 or2; if y is 1, z=1 and if y=2, z=0.

Illustrative specific compounds falling into this class are the following:

CHzOO OH CHzCOOH CHzC O OH CH2C OHzNCrzHzs CHzC O OHsCnHn CHzC 0 OH NC12H25 CuHzs-N-CHz-CHz-N 01120 O OH These materials are generically described as alkylamine salts of alkyl irnino polyacetic acids.

These processing aids may be incorporated into the rubber polymer which is to be used as the binder component for a magnet stock in any conventional manner such as by mill-mixing or mixing in an internal mixer such as the Banbury.

In the practice of this invention it is desirable to use from about 4 to about 10 parts by weight of processing aid per 100 parts by weight of rubber polymer.

The preferred magnetic powder for use in mixing these flexible magnet stocks is barium ferrite. The particle size is preferably ultrafine, from about 0.5 micron to about microns in diameter. The general formula is BaFe O Strontium ferrite or other ferromagnetic powders may also be used. The magnetic properties of the NBR flexible magnets are determined on extruded strips about 0.13 in. thick and 0.35 in. wide. The strips are magnetized to saturation with a coil magnetizer that is designed to provide a concentration of strong alternating north and south poles along one of the faces of the strip; opposing weak south and north poles exist on the opposite parallel face. The maximum pull strengths in pounds attained across a 0.015-inch air gap are determined for both the magnetically strong and weak sides of the magnetized strips. The strips are one foot long, so that the strengths are in pounds per foot. Because of the geometry of the pole arrangement, the maximum pull strength measured for the strong side is a measure of its ability to serve in a latch-magnet application; the stronger the pull strength, the stronger the strength of the magnet in a latch-type application.

The maximum energy product, (BH) max., which corresponds to the point on the demagnetization portion of the hysteresis loop which will give the maximum energy output per unit volume of magnetic material external to the magnet, is determined with a standard magnetic permeameter. This property is an important daign factor in specifying permanent magnets in electrical applications such as to provide field excitation in DC. and A.C. motors and generators.

Oil resistance of flexible magnets is evaluated by immersing them for six days in type A automatic transmis- The present invention Will be further illustrated by the following examples wherein the amounts of the various ingredients are expressed in parts by weight unless otherwise indicated.

PREPARATION OF PROCESSING AIDS The mono-octadecylamine salt of dodecyliminodiacetic .acid is prepared by dissolving 3.24 lb. of octadecylamine in 10.6 lb. of absolute ethanol. The solution is heated to C. and 3.6 lb. of dodecyliminodiacetic acid is added stepwise within 15 min. The reaction solution is maintained at 75 C. for an additional 10 min. Crystallization of the solid product is effected by pouring the hot solution into a stainless steel container and cooling it to 5-l0 C. The insoluble solid product is removed by filtration on a Buchner funnel. The product is Washed twice with ethanol, air dried overnight, and vacuum dried (15 mm. of Hg) at 50 C. A yield of 6.3 lb. of the mono-octadecylamine salt of dodecyliminodiacetic acid is obtained and designated as processing aid (A).

The di-octadecylamine salt of dodecyliminodiacetic acid (B) and the mono-dodecylamine salt of dodecyliminodiacetic acid (C) are prepared in a similar manner.

A processing aid having the structure CHzCOOH wherein R is a mixture of alkyl groups having an average of 18 carbon atoms is prepared as follows: Chloroacetic acid (2.24 moles) in 400 ml. of methanol is neutralized with 31% NaOH solution. Duomeen T wherein R is a mixture of alkyl groups having an average of 18 carbon atoms, 0.25 mole) is added. The reaction mixture is brought to 7073 C. and the pH of the reaction mixture is maintained at 8-10 by the addition of more 31% NaOH solution until the pH becomes fairly constant for a period of time. The mixture is cooled and the product is precipitated with hydrochloric acid (pH of 2). The solid is isolated by filtration, washed and dried.

19.9 g. of the reaction product and 25.0 g. of octadecylamine are dissolved in m1. of hot absolute ethanol. Heating the solution over a water bath precipitates the desired salt and removes most of the ethanol. The remainder of the ethanol is removed in a vacuum desiccator. The solid product is dried 4 hours at room temperature in a vacuum oven.

The yellow-orange powdery product analyzes to be the di-octadecylamine salt of octadecylpropylene diaminetriacetic acid with the formula CHzOOOH C1sHs7N-CH2CH2CH2N(CH2C O OHaNCisHQ'I): and is designated processing aid (D).

EXAMPLE A charge of 77.2. g. of a commercial butadieneacrylonitrile copolymer, analyzing 45% butadiene, 55% acrylonitrile, is set up on a rolling rubber mill at F. 7.1 g. of the reaction product of octadecylamine and dodecyliminodiacetic acid (A), formula CHzC O OHaN C18H31 C12H25N CHzCOOH are added to the rubber and milled in over a period of about 2 min. Next 739.4 g. of ultrafine barium ferrite are added and milled into the rubber. Total milling time is about 15 min. This amounts to 62 volume percent barium ferrite in the rubber binder. The flexible sheet stock is easily extruded into a smooth, flexible strip through a one inch die producing a strip .38" wide and .13" thick at 170-240 F. Maximum pull strength, energy product and oil resistance are determined on the magnetic strips produced. Data are set forth at Run 1 in Table 1.

Similar magnetic strips are made using the same procedure except for the substitution of processing aids (B) and (C) for processing aid (A) in Runs 2 and 3. In Run 4 a commercial nitrile rubber copolymer analyzing 55% butadiene, 45% acrylonitrile by weight is employed as the binder stock and the di-octadecylamine salt of octadecylpropylenediaminetriacetic acid (D) is used as the processing aid. Data are set forth in Table 1. The control magnet is a standard commercial flexible magnet containing 623 vol. percent BaFe O and based on a chlorosulfonated polyethylene-butene rubbery copolymer binder.

yis1andzis0;whenxis1,yis1or2;ifyis1,z=1 and if y is 2, z=0.

2. The method of making a flexible magnetic structure comprising mixing together butadiene-acrylonitrile rubber copolymer as a binder, barium ferrite as a magnetic powder and as a processing aid, a material having the formula where R is a hydrocarbon group having from 6 to 20 carbon atoms, R is selected from the group consisting of hydrogen, CH COOH, and CH COOH NR', R" is a saturated hydrocarbon group having from 2 to 10 carbon atoms, R' is a hydrocarbon group having from 6 to 20 carbon atoms, x is a number from 0 to 1, y is a number from 1 to 2 and z is a number from 0 to 1; when TABLE 1 Processing Max. pull (BH) max. Tensile Volume, Run No Aid strength (gauss- (p.s.i.) percent Appearance lb.) oersteds) swell 3. 790,000 815 1. 85 Excellent. 2. 99 1, 150 1. 50 Do. 2. 83 760, 000 688 1. 17 Do. 2. 77 740, 000 53 3. 11 740, 000 1, 400 97. 3 Dlstended.

I claim:

1. A magnetic structure comprising 100 parts by weight of butadiene-acrylonitrile rubber copolymer as binder, at least 60 volume percent barium ferrite as magnetic powder, and as a processing aid from 4 to 10 parts of a material having the formula where R is a hydrocarbon group having from 6 to 20 carbon atoms, R is selected from the group consisting of 4 xis0,yis1andzis0;whenxis l,yis1or2;ifyis1, 2:1 and if y is 2, 2:0, extruding said mixture through a die to form a shaped strip and cutting said shaped strip to a desired length.

References Cited UNITED STATES PATENTS 3,117,092 l/1964 Parker 252-6254 3,121,131 2/ 1964 Blume 264111 3,184,807 5/ 1965 Shornstheimer et al.

' 252-62.54 3,228,904 1/ 1966 Morris et a1. 260534 ALLAN LIEBERMAN, Primary Examiner.

S. L. FOX, Assistant Examiner.

US. Cl. X.R.

from 1 to 2 and z is a number from 0 to 1; when x is 0, 260-31.2 

